Omnipolarized antenna horn



PARISI OMNIPOLARZED ANTENNA HORN May s, 1962 3 Sheets-*Sheet l Filed May 28, 1957 May 8, 1962 F. E. PARISI 3,034,118

OMNIPOLARIZED ANTENNA HORN Filed May 28, 1957 3 Sheets-Sheet 2 IN VEN TOR.

FRANK E. PAR ISI [rt-9 9 f BY ATTORNEY May 8, 1962 F. E. PARISI oNNIPoLARIzED ANTENNA HORN 3 Sheets-Sheet 3 Filed May 28, 1957 INVENTOR.

FRANK E. PARISI BY ATTORNEY 3,034,118 OMNRPOLARIZED ANTENNA HRN Frank E. Parisi, Waban, Mass., assignor to General Electronic Laboratories, lne., Cambridge, Mass., a corporation of Massachusetts Filed May 28, 1957, Ser. No. 664,872 14 Claims. (Cl. SM1-100) This invention relates to antennas and more particularly to horn type, broad band antennas for omnipolarized radiation.

A single, compact antenna horn or package capable of receiving or transmitting a wide range of microwave frequencies regardless of polarization is desirable in the field of electromagnetic wave communication. Itis particularly desirable in military operations for countermeasures activities. For maximum usefulness in this eld, it should be capable of not only operating over a wide range of frequencies, but also have a high sensitivity to both right and left hand circularly polarized, as well as linearly polarized, radiation.

Accordingly, a primary object of the present invention is the provision of a microwave antenna for use with electromagnetic radiation over a wide range of frequencies regardless of the sense of polarization of the radiated energy.

Another object is the provision of an antenna for electricaliy polarized radiation which is capable of being selectively switched for operation between left and right senses of polarization.

A still further object is the provision of a horn ,type microwave antenna for transmitting selectively left or right hand circularly polarized radiation and for receiving electromagnetic radiation regardless of the sense of polarization, including circular or elliptical polarization of either sense as well as linear polarization of any orientation.

And a still further object is the provision of a broadband, horn type antenna compable of transmitting and receiving highly directional microwave radiation.

Another object is the provision of a horn type, broadband, microwave antenna having incorporated therein as an integral part thereof, a bridge feed to effect proper conditions for the production of elliptically polarized radiation.

And a further object is the provision of a broadband antenna comprised of a pair of coaxially arranged horns, cach capable of operation with `ornnipolarized radiation over a preselected portion of the overall range of frequencies and which lend themselves to rugged, durable construction for operation alone or with suitable reflectors.

Another object is the provision of a horn type antenna having two independent channels in the same structure, the channels lending themselves for use with such combinations as a pair of receivers or transmitters, or one receiver and one transmitter, or a pair of receivers wherein one is a broadband receiver and the other is a highly selective receiver.

A still further object is the provision of a pair of horn type antennas in a single coaxial structure, with each horn having two independent channels or a total of four independent channels in a single structure for selectively receiving and transmitting electromagnetic wave signals.

These objects, features and advantages are achieved generally by providing a horn loaded in one plane with dielectric material having the equivalent of substantially a quarter wavelength phase change in the radiation passing through it as compared to the radiation in a plane perpendicular to the dielectric loaded plane, and a coaxial line 3,t}34,l 18 Patented Mayr-8,1962

tion between the two, operation with right and-left hand circularly polarized radiation is thereby achieved.

By providing a second, smaller horn in the unused center portion of the first horn, with Vboth horns in coaxial relation to each other and with each horn arranged for operation over a selected band of frequencies, a much broader band of overall operation is thereby achieved'.

By making the horn feed in the formof a coaxial line with a gap at the axis of the horn between the outer coaxial cable and increased diameter inner cable, balanced voltages are developed in the waveguide to excite the desired mode.

Byilaring the aperture at the open end of the outer horn, the primary radiation pattern is further controlled'.

By adding dielectric kmaterial to the open end ofthe inner horn of the coaxial arrangement, additional control of the inner horn radiation is achieved.

These and other objectsyfeatures and advantagesof the invention will become more apparent from the following description of preferred embodiments of the invention and wherein:

FIG. l is a diagrammatic cross sectional representation taken on line 1--1 of FIG. 2 and illustrating a coaxial horn made in accordance with the present invention;

FG. 2 is a cross section taken on line 2 2 of FIG. 1 to more clearly show construction;

FIG. 3 is a segmentary cross sectional View to enlarged scale taken on line 3 3 of FIG. 2 to more clearly show construction ofthe inner horn feed;

FIG. 4 is a schematic representation ofa bridge feed Y arrangement for achievingY polarized radiation and illustrating operation of applicants invention;

FIG. 5 is a section'on line-5 5 of FIG. 6 illustrating a mechanical arrangement of applicants invention which combines features of the four waveguides and bridge shown in Fl-G. 4 'into a simplified physical structure;

FIG. 6 is a cross section on line 6--6 of FIG. 5;

FIG. 7 is a cross section on line 7--7 of FIG. 5 particularly illustrating the coaxial line feed system;

FIG. 8 is a cross section on line 8 8 of FIG. 5- showing the feed system for polarization in the opposite sense to that in FIG. 7;

FIG. 9 is a segmentary view taken on line 9-9 of FIG. 2 to show feed construction.

Referring rst to FIG. 4,- a horn feed arrangement illustrating the theoryof operation of applicants invention is designated generally by the numeral 10. The feed 1t) is applied to four ridge loaded waveguides 12, 14, 16 and 18 having ridges 11, 13, 15 and 17 respectively appearing in cross section in FIG. 4. The waveguides 12 and 14 are arranged in opposed relation and the wave- H commercially as Teflon.

About the waveguides are an'inner coaxial ring 22 and outer coaxial feed lines' 24 and 26 forming a bridge network 28. Waveguides 12, 13, 14 and 16 are connectedV through waveguide to coaxial junctions' to taps or points 3i), 32, 34 Vand 36 respectively on the inner cable of the coaxial line 22 and are equally spaced about the inner coaxial feed ring Z2. A microwave signal device 35 is connected through a voltage balancing structure, herein termed a balun 37, andthe coaxial feed line 24 to a point 38 on the inner feed ring 22, midway betweenthe taps 34 and ,36 for the waveguides 14 and l16 respectively, and

3 the point 40 midway between the taps 3G and 32 for the other two waveguides 12 and 1S respectively. The signal device 35 may be a signal generator or signal receiver depending on whether the horn 1d is used for transmitting or receiving signals as will be hereinafter described.

In similar manner, another signal device 39, similar to the signal device 3S, is connected through a balun 41 and the coaxial feed line 26 to a point 44, between the junctions 32 and 34 for the waveguides 13 and 14, and the point 46 between the junctions 3i) and 36 of the waveguides 12 and 16 respectively.

In the operation of the horn feed 1G, with only the signal device 39 operating as a generator to energize the circuit, it will be noted that the appearance of a positive potential at point 46 and a negative potential at point 44 will cause the points 30 and 36 to be positive with equal amplitudes and the points 32 and 34 to be negative with equal amplitudes. The points 3S `and 40 will be at zero potential. The transmission line 24 will therefore have no eiect on the signals of the generator 39. Resulting excitation of the waveguides 12 and 16, and 14 and 18 will be in two perpendicular mode orientations which add vectorially to produce a resultant field with a space orientation represented by a vector 42.

Visualizing the resultant radiation designated by the vector 42 as coming upwardly out from the plane of the paper, radiation from the waveguides 12 and 14 will be delayed ninety degrees because of the quarter wavelength increase in electrical length caused by the dielectric materials 23 and 25. Circularly polarized radiation with a clockwise or right hand sense is thereby obtained. This is because the vector 42 is the resultant of two vectors which are in space quadrature due to the geometrical arrangement of the waveguides 12, 14, 16 and 18, and in time quadrature due to the diderence in electrical length between the pairs of waveguides 12 and 14, and 16 and 18 respectively.

Similarly, when the other signal generator 35 excites the circuit lil, the points 44 and 46 will be at zero potential and the feed line 26 will have no affect on the generated signal. A resultant field with a space orientation represented by a vector 43, which is rotated in space by an amount Si? which is ninety degrees from the vector 42, will occur. Again, because of the quarter wavelength delaying effect of the dielectric materials 23 and 25 in the waveguides 12 and 14, the resultant radiation vector 43 will be circularly polarized. But in this instance, it will be circularly polarized in a left hand sense. It will be noted that changing operation from signal generator 39 to 35 can be viewed as introducing an additional one hundred and eighty degree phase delay. Hence, it has the effect of reversing the sense of tbe circular polarization.

While the above discussion related to signal generators 39 and 35 and to transmission of radiation, the principles are the same for receiving radiation. For receiving radiation, the signal generators 35 and 39 would be suitable receivers instead. The explanation here given was in terms of transmitting rather than receiving because of ease of presentation. However, it should be understood that the arrangement may operate for receiving electromagnetic radiation as well as transmitting and that the signal devices 35 and 39 refer to either signal generators or signal receivers. In some instances it may be desirable to have one receiver as 35 a broad band receiver for broad search coverage and the other receiver as 39 a highly selective receiver for increased sensitivity to a selected frequency. Also, in some instances it will be desirable to use both a transmitter and receiver with the same horn. Thus, one of the signal devices as 35 may be a transmitter and the other signal device as 39 may be a receiver, or vice versa.

Referring now to FIG. 5, a` simplified mechanical arrangement and modification over that of the representation in FIG. 4 is designated generally by the numeral 48.

The simplified mechanical arrangement 4S in FIG. 5 succeeds in combining the four waveguides 12, 14, 16 and 13, bridge feed arrangement 1) and baluns 37 and 41 of FIG. 4 into a unitary, integrated structure. This structure contains the electrical equivalent of FIG. 4 as an irnproved mechanical configuration.

The mechanical coniguration 4S in FIG. 5 comprises a cylindrical outer shell or waveguide 52 of conductive material as brass or copper with a closure 54 of similar material at the back end. The front end 56 is open. Set centrally of the shell or waveguide 52 is a filler 5S of conductive material such as copper or brass.

The filler 58 has an axis 69 coinciding with the axis of the circular housing 52. The rearward portion of the filler S8 may be of increased diameter, circular cross section with openings 62 and 64 at right angles to each other and transverse to the axis 60. The openings 62 and 64 house feed systems 66 and 68 for exciting left and right hand circularly polarized radiation respectively, as will be hereinafter more fully described. The upper portion of the filler 58 is cut away to form raised sections having four surfaces 70, '71, 72 and 73 disposed in pairs 70, 72 and 71, 73 in opposite relation to each other to provide ridge loading in the waveguide or shell 52' forming two pairs of ridges in substantially perpendicular relation to each other and having functions comparable to the four waveguides described in connection with FIG. 4, but combined in FIGS. 5 and 6 without lateral metallic boundaries.

Between the two opposed ridges 71 and 73 and the outer shell 52 are placed solid dielectric radiation phasing inserts 75 and 77 respectively of such material as Teflon. The inserts 75 and 77 are of a length corresponding to the dielectric inserts 42 and 43 respectively in FIG. 4 to provide quarter-wave electric phase differentials between the radiation passing through them and that emanating from the space between the ridges 70, 72 and the outer shell or waveguide 52.

The feed system '66 includes an outer coaxial line 74 of electrically conductive material as brass or copper anchored in electrically conductive engagement with the waveguide 52 yat its point of entrance. The outer coaxial line or conductor 74 terminates near the axis 69 of the waveguide shell 52 to form a centrally located gap 76 with one end of an anchoring stem 78 of conductive material. The other end of the stem 73 is iixed in electrical engagement with the waveguide shell 52 at a point 180 degrees from that at which the outer conductor 74 is anchored. The feed system 66 also has an inner coaxial conductor Sil passing centrally inside the outer coaxial conductor .'74 and in electrical engagement with the free end of the anchoring stem '78. The ends of the coaxial conductors 74 and 8G outside the waveguide shell 52 may be connected to a receiver or signal generator as 35 or 39 in FIG. 4, depending upon whether transmitting or receiving electromagnetic radiation is desired as described in connection with FIG. 4.

The small diameter coaxial line portion Si? of the feed system 66 forms a type of `balun that is well suited to the mechanical structure 4S. It shows most cleanly in FIG. 7. The unbalanced voltage in the small diameter coaxial line 80 appears across the gap 76 in the center at the axis 60 of the waveguide shell 52 and feeds the larger diameter coaxial line 74 and anchoring stem 78 with balanced (equal and opposite) voltages which develop between the waveguide shell 52 and ridges 7u, 71, 72 and 73 to excite the waveguide in corresponding perpendicular component orientations of the desired mode. This excitation by the feed system 66 produces polarized radiation in a left hand sense in manner comparable to that described in connection with FIG. 4.

The feed system 68 is constructed similarly to that of the feed system 66 and produces excitation in the same manner except that it is displaced ninety degrees with respect to the feed system 66 and effects a right hand circular polarization as described in connection with FIG. 4. While the feeds 66 and 68 lie in planes different distances from the closure '54, it has been found that vboth feeds should preferably be in the same plane as shown and described hereinafter in connection with FIG. 1.

The parts shown in FIGS. 5, 6, 7 and S, together with a flared aperture, as will be described in connection with FIG. 1, for matching impedance with space and for controlling the primary radiation pattern constitute a single horn for selectively transmitting left and right hand elliptically polarized radiation or receiving elliptical-ly or linearly polarized radiation of any sense or orientation.

A second, smaller horn placed in the unused center portion S2 of the ller 58 forms a compiete coaxial horn system operable over a wider range of frequencies than possible with a single horn. Such a coaxial horn will hereinafter be more fully described in connection with FIG. 1.

Ridge loading of the waveguide has been herein preferably used because of its desirable properties. It effects a lower cutoii frequency ofthe desiredmode, thereby allowing a smaller waveguide to be used for a given frequency range. It also has the desirable property of raising the cutoff frequency of the second order mode whichis an undesired mode, to thereby permit operationover a wider range of frequencies. It also effects a lower characteristic impedance, making it easier to obtainya match with the coaxial output.

Referring to FIG. l in more. detail, a pair yof coaxial horns made in accordance with the present invention and utilizing principles discussed in connection with FIGS. 4 and 5 is designated generally lby the numeral 86. The coaxial horns 86 are comprised of an outerhorn 36 having an octagonal cross sectional waveguide shape, and an inne-r horn 90 having a square waveguide cross sectional shape. The horns S8 and 90 have a corn-mon axis 92. The use of octagonal and square cross sectional waveguide shapes are the result of compromise from circular waveguides to achieve ease in fabrication.

The body of the outer horn 88 is a length of cctagoual waveguide of conductive material as brass or copper loaded with oppositely disposed pairs of ridges 94, 98 and 96, 100 (FIG. 2) of similar material and placed at right angles to each other about the axis 92. The wave guide 88 has a closure 102 of conductive material at one end and an outward horn are opening 104 at the other end. The horn flare 104 serves to achieve a suitable primary radiation pattern and a suitable impedance match between the waveguide 88 and space.

Solid dielectric polarizers 106 and 108 as Teflon or other suitable material are placed between the ridges 94 and 98 respectively in the body of the `outer horn 8S. They are of a length 109 to establish the required space and time relationship between the electric field vectors of the desired mode orientations for electrical polarization over the operating frequency range as discussed in con-t nection with FIGS. 4 and 5. Both the ridges 94 and 98 are undercut by an amount 110 (FlG. 1) running the length of the s-olid dielectric polarizers 106 and 108 to maintain a constant characteristic impedance.

The outer horn 88 also includes near its yback end, a pair of feeds 112 and 114 at right angles to each other mounted in suitable transverse openings in a plate 1-16 of conductive material anchored in conductive engagement with the back ends of the ridges 94, 96, 98 and 100 and through a hollow axial conductor 11S to the back end closure 102. The feeds 112 and 114 are similar in construction to those described in connection with FIGS. 7 and 8 and include an outer coaxial conductor 120 in electrical engagement with the waveguide 88 and terminnating at the axis 92 ata dielectric spacer support 122. The feed 112 also includes an inner coaxial conductor 124 in electrical engagement with the upper end of a solid conductor rod 126 extending from the spacer 122 and tenninating on the opposite side of the waveguide S8 in substantially the same plane 128 as that of the outer coaxialcon-y ductor 120.

Similarly the feed 112 has an outer and inner coaxial conductors 130 and 132 respectively, lsimilarly yanchored in eectrical engagement with the waveguide 88 in the same plane 125 as the feed 112. However, to avoid physical interference with the feed 112, the feed 114 at the axis92 is offset from the feed `112 so that its dielectric spacer support 134. is offset from the dielectric spacer support 122, as shown in FIGS. l and 9. Y

The inner horn 90, with some structural differences as will be herein described, is essentially a smaller version of the large horn 88. It includes a square waveguide and a solid core 136 of electrically conductive material. The Vsolid core 136 has about its periphery oppositely disposed ridges 138, 140, 142 and 144 arranged` in pairs at right angles to each other. Solid dielectric polarizers 146 and 148 of such material as Teflon are placed between the ridges 142 and 144 respectively and respective iats ofthe waveguide 135 to produce elliptically polarized radiation from the horn 90, as described in connection with FIGS. 4 and 5. The ridges 142 have undercut portions 150 running the length of the dielectric polarizers 146 and 148 for maintaining constant impedance. The horn 90 also includes a closure 152 of conductive material at its back end to provide a backup cavity 153 for a pair of feeds 154 and 156 which are quite similar to the feeds 112 and 114. The feeds 154 and 156 include outer coaxial conductors 155 and 157 and inner conductors 159 and 161 respectively. Both feeds ,154"V and 156 are in electrical engagement with the waveguide 135 at the same plane 163. The outer conductors 155 and 157 are bent at the axis 92 to avoid physical interference. They are also provided with dielectric spacer inserts or supports 165 and 166 respectively similar in construction and purpose to the inserts 122 and 134 described above in connection with the feeds 112 and 114 for the horn 88.

The ridges 140, 142, 144 and 146 are preferablyarranged with an inward taper 168 at the forward end to produce improved aperture match. Since an` outward flare 158 at the forward end of the inner horn 90 has a detrimental effect on the match of the outer horn aperture 104, the flare 158 of the inner horn is kept at a minimum. To reduce the size of the are 158 of the inner horn and still insure good inner horn radiation patterns and aperture match, solid dielectric loading 160 with such material as Teon is used. The dielectric loading 160 has the added advantage of assisting in the match of the n outer horn to space. This solid dielectric loading 160 is retained in place by a metal tip 162 and screw 170 in the front end of the core 136.

The, placement of the inner hornv 90 with respect to the outer horn 8S is determined by the range of fre- Y quencies handled by each horn because the center of radiation of each of the horns varies as the frequency changes. A polystyrene radome 164 at the open end of the ilare 104 of the outer horn may be used to provide a suitable closure for protecting the entire assembly 86 from the weather. l

Feeds 112, 114, 154 and 156 may be connected to suitable radio signal generators or receivers 35 and 39 as described in connection with FIG. 4, depending upon whether the transmission or reception or combined reception and transmission of omnipolarized radiation, as explained in connection with FIG; 4, is desired. Thus, the horn structure 86 achieves four independent channels inasingle compact structure for use With receivers ortransmitters suitable for other frequency ranges ofi operation where desired. This invention is not limited to the specific details of construction and operation as equivalents will suggest themselves to those skilled in the art.

What is claimed is:

l. In a horn for electromagnetic wave radiation, the combination of a waveguide, means for excitation of the waveguide in two transverse mode orientations having a definite wave phase relationship, ridges inside of and in spaced relation to said waveguide aligned with said mode orientations, and means including dielectric phase shift material between the ridges and the waveguide in one of the mode orientations for shifting the wave phase in said one of said mode orientations with respect to the wave phase in the other mode orientation.

2. In a horn for electromagnetic wave radiation, the combination of a waveguide, means for excitation of the waveguide in two perpendicular mode orientations having a definite wave phase relationship, ridges inside of and in spaced relation to said waveguide aligned with said mode orientations, and means including dielectric phase shift material between the ridges and the waveguide in one of the mode orientations for shifting the wave phase in said one of said mode orientations by a quarter wave period with respect to the wave phase in the other mode orientation.

3. In a horn for electromagnetic wave radiation, the combination of a waveguide, a pair of feed means coupled to said waveguide, each feed means oriented for excitation of the waveguide in two transverse mode orientations having a definite wave phase relationship, means including dielectric phase shift material in said waveguide for shifting the wave phase in one of said mode orientations of each feed means with respect to the wave phase in the other mode orientation.

4. In a horn for electromagnetic wave radiation, the combination of a waveguide, a pair of feed means coupled to said waveguide, each feed means arranged for excitation of the waveguide in two perpendicular mode orientations having an in phase wave relationship, means including dielectric phase shift material in the waveguide for shifting the wave phase of one of said perpendicular mode orientations of each feed means by a quarter wave period with respect to the wave phase of the other respective mode orientation, and a half wave period between the phase shift in said one mode orientation of one of the feed means and the one mode orientation of the other feed means.

5. In a horn for electromagnetic wave radiation, the combination of an octagonal sided waveguide of electrically conductive material having a closure at one end and `an impedance matching ared opening at the other end, four ridge members of electrically conductive ma terial inside said octagonal waveguide, one of said ridge members in spaced relation to each of alternate internal sides of the octagon defining two sets of opposed ridges with one set disposed in substantially perpendicular relation to the other set, the space between the two opposed ridges in one set and the corresponding sides of the waveguide being loaded with solid dielectric material for changing the phase of waves passing therethrough with respect to waves passing through the space between the other pair and the waveguide, and a coaxial to waveguide transition having an inner and outer conductors in transverse relation to said waveguide at a position distal from said closure, one of said conductors coupled to a hexagon side midway between two adjoining ridges and the other conductor coupled to an opposing hexagon side.

6. In a horn for electromagnetic wave radiation, the combination of a waveguide of electrically conductive material having a closure at one end and an impedancey matching ared opening at the other end, four ridge members of electrically conductive material in said waveguide, said ridge members disposed in opposed pairs spaced from said waveguide with one pair in substantially per- 8 pendicular relation to the other pair, the space between the two opposed ridges in one pair and the waveguide being loaded with solid dielectric material for changing the phase of waves passing therethrough with respect to waves passing through the spaceV between the other pair and the waveguide, and a waveguide transition coupled to said waveguide at a position distal from said closure.

7. In a horn for electromagnetic wave radiation, the combination of a waveguide of electrically conductive material having a closure at one end and an impedance matching flared opening at the other end, four ridge members of electrically conductive material in said waveguide, said ridge members disposed in opposed pairs spaced from said waveguide with one pair in substantially perpendicular relation to the other pair, the space between the two opposed ridges in one pair and the waveguide being loaded with solid dielectric material for changing the phase of waves passing therethrough with respect to waves passing through the space between the other pair and the waveguide, and a waveguide transition coupled to said waveguide at a position distal from said closure, said transition being in a plane midway between two adjacent ridges.

8. In a horn -for electromagnetic wave radiation, the combination of a waveguide of electrically conductive material having a closure at one end and an impedance matching ared opening at the other `end, four ridge members of electrically conductive material in said waveguide, said ridge members disposed in opposed pairs spaced from said waveguide with one pair in substantially perpendicular relation to the other pair, the space between the two opposed ridges in one pair and the waveguide being loaded with solid dielectric material for shifting the phase of waves passing therethrough with respect to waves passing through the space between the other pair and the waveguide, and two waveguide transitions coupled to said waveguide at positions distal from said closure, one of the transitions being in a plane midway between two adjacent ridges, the other transition being in a plane at right angles to said one transition plane.

9. A horn for electromagnetic wave radiation comprising a waveguide of electrically conductive material about an axis and having a closure at one end and an impedance matching flared opening at the other end, four ridge members of electrically conductive material about said axis in said waveguide, said ridge members disposed in opposed pairs spaced from said waveguide with one pair in substantially perpendicular relation to the other pair, the space between the two opposed ridges in one pair and the waveguide being loaded with solid dielectric material for shifting the phrase of waves passing therethrough with respect to waves passing through the space between the other pair `and the waveguide, and two waveguide transitions coupled to said waveguide at positions distal from said closure, one of said transitions oriented for circularly polarized radiation in one rotational direction, the other transition oriented for circularly polarized radiation in the opposite rotational direction.

l0. A pair of horns, each as in claim 9, one being inside the other on the same axis with the inner horn scaled dimensionally for one band of frequencies and the other scaled dimensionally for another band of frequencies.

1l. In combination, a horn for electromagnetic wave radiation, means in said horn for elliptically polarizing Wave radiation in one rotational direction, means in said horn for elliptically polarizing wave radiation in the opposite rotational direction, a pair of electric signal devices, and means coupling one of said signal devices to one of said polarizing means and the other of said signal devices to the other polarizing means.

12. The combination as in claim ll wherein one of the signal devices is a broad band receiver and the other is a highly selective receiver.

13. The combination as in claim ll wherein one of the signal devices is a receiver and the other is a signal generator.

14. In a horn for electromagnetic Wave radiation, the

combination of a waveguide, four radiation means in opposed pairs about an axis inside said waveguide to form with said waveguide four Wave directing means having open ends facing in the saine direction, means in a pair of said opposed directing means for changing the phase of the wave radiation by av preselected value with respect to the radiation in the remaining pair of directing means, a pair of signal conducting means, and

` References Cited in the le of this patent UNITED STATES PATENTS 2,530,818 FOX NOV. 21, 1950 2,669,658 Jackson 1 Feb. 16, 1954 2,741,744 Driscoll Apr. 10, 1956 2,851,681 Cohn Sept. 9, 1958 i 2,866,972 Anderson Dec. 30, 1958 

